A Compend of Human Physiology Especially Adapted for the Use of Medical Students
Journal: JAMA (1901)

This may naturally be divided into:1. Individual physiologyy the object of which is a study of the vital phenomena or functions exhibited by the organs of any individual animal.2. Comparative physiology, the object of which is a comparison of the vital phenomena or functions exhibited by the organs of two or more ani- mals, with a view of unfolding their points of resemblance or dissimilarity.Human physiology is that department of physiologic science which has for its object the study of the functions of the organs of the human body in a state of health.If the body of any animal be dissected, it will be found to be composed of a number of well-defined structures, such as heart, lungs, stomach, brain, eye, etc., to which the term organ was originally applied, for the reason that they were supposed to be instruments capable of performing some important act or function in the general activities of the body.Though the term organ is usually employed to designate the larger and more familiar structures just mentioned, it is equally applicable to a large number of other structures which, though possibly less obvious, are equally important in maintaining the life of the individual e.g., bones, muscles, nerves, skin, teeth, glands, blood-vessels, etc.Indeed, any com- plexly organized structure capable of performing some function may be described as an organ.A description of the various organs which make up the body of an animal, their external form, their internal arrangement, their relations to one another, constitutes the science of Animal Anatomy.This may naturally be divided into : 1.Individual anatomy, the object of which is the investigation of the construction, form, and arrangement of the organs of any individual animal.2. Comparative anatomy, the object of which is a comparison of the organs of two or more animals, with a view of determining their points of resemblance or dissimilarity.If the organs, however, are subjected to a further analysis, they can be resolved into simple structures, apparently homogeneous, to which the name tissue has been given e.g., epithelial, connective, muscle, and nerve tissue.When the tissues are subjected to microscopic analysis, it is found that they are not homogeneous in structure, but composed of still simpler elements, termed cells and fibers.The investigation of the inter- nal structure of the organs, the physical properties and structure of the tissues, as well as the structure of their component elements, the cells and fibers, constitutes a department of anatomic science known as Histology, or as it is prosecuted largely with the microscope, Microscopic Anatomy.HUMAN PHYSIOLOGY character, whereby a part at least of the food material furnished by the blood-plasma is transformed through a series of ascending chemic stages into living material, and whereby it is repaired and its former physio- logic condition restored.It is, therefore, said that the living material undergoes molecular integration as a preparation for functional activity.To these changes the term anaholism is also applied.During the course of its physiologic activities the cell bioplasm produces materials of an entirely different character which vary with the cell, such as fat, glycogen, mucigen, pigments, ferments, etc., which are generally spoken of as metabolic products.Living material has also a temperature varying in degree in different species of animals as well as in different parts of the same animal.Here as elsewhere the temperature is due to heat liberated from organic compounds through disruption and subsequent oxidation to simpler compounds.Though some of the heat liberated may come from the tissue molecules, the larger part by far comes from the food molecules-sugar, fat, and protein, constituents of the fluids circulating in the tissue spaces.These foods carry into the body potential energy, ultimately derived from the sun.Whey they are disrupted and oxidized the potential energy is transformed into kinetic energy which manifests itself for the most part as heat.To the sum total of all the chemic changes occurring in tissues and foods the term metabolism is given.Physiologic Properties of Protoplasm.-All living protoplasm possesses properties which serve to distinguish and characterize it-viz., irritability, conductivity, and motility.Irritability, or the power of reacting in a definite manner to some form of external excitation, whether mechanical, chemic, or electric, is a funda- mental property of all living protoplasm.The character and extent of the reaction will vary, and will depend both on the nature of the proto- plasm and the character and strength of the stimulus.If the protoplasm be muscle, the response will be a contraction; if it be gland, the response will be secretion; if it be nerve, the response will be a sensation or some other form of nerve activity.Conductivity^or the power of transmitting moleculat disturbances arising at one point to all portions of the irritable material, is also a char- acteristic feature of all protoplasm.This power, however, is best de- veloped in that form of protoplasm found in nerves, which serves to transmit, with extreme rapidity, molecular disturbances arising at the periphery to the brain, as well as in the reverse direction.Muscle protoplasm also possesses the same power in a high degree.II the skeleton, especially in its relation to joints, will be referred to which underlie and determine both the static and dynamic states of the body.Structure of Joints.-Thestructures entering into the formation of joints are :1. Bones, the articulating surfaces of which are often more or less ex- panded, especially in the case of long bones, and at the same time variously modified and adapted to one another in accordance with the character and extent of the movements which there take place.2. Hyaline cartilage, which is closely applied to the articulating end of each bone.The smoothness of this form of cartilage facilitates the move- ments of the opposing surfaces, while its elasticity diminishes the force of shocks and jars imparted to the bones during various muscular acts.In a number of joints, plates or discs of white fibro-cartilage are inserted between the surfaces of the bones.3. A synovial membrane, which is attached to the edge of the hyaline cartilage entirely inclosing the cavity of the joint.This membrane is composed largely of connective tissue, the inner surface of which is lined by endothelial cells, which secrete a clear, colorless, ^viscid fluid-the synovia.This fluid not only fills up the joint-cavity, but, flowing over the articulating surfaces, diminishes or prevents friction.4. Ligaments-tough, inelastic bands, composed of white fibrous tissue -which pass from bone to bone in various directions on the different aspects of the joint.As white fibrous tissue is inextensible but pliant, ligaments assist in keeping the bones in apposition, and prevent displace- ment while yet permitting of free and easy movements.Classification of Joints.-Alljoints may be divided, according to the extent and kind of movements permitted by them, into (i) diarthroses;(2) amphiarthroses; (3) synarthroses.A. Diarthroses.-Inthis division of the joints are included all those which permit of free movement.In the majority of instances the articu- lating surfaces are mutually adapted to each other.If the articulating surface of one bone is convex, the opposing but corresponding surface is concave.Each surface, therefore, represents a section of a sphere or cylinder, which latter arises by rotation of a line around an axis in space.According to the number of axes around which the movements take place all diarthrodial joints may be divided into:I. Uniaxial Joints.-Inthis group the convex articulating surface is a segment of a cylinder or cone, to which the opposing surface more or less head, with inclination to either side.When the surfaces do not take the same direction, the joint, from its resemblance to the surfaces of a saddle, is termed a saddle-joint e.g., the trapezio-metacarpal.The movements permitted by this joint are also flexion, extension, adduction, abduction, and circumduction.3. Polyaxial Joints.-Inthis group the convex articulating surface is a segment of a sphere, which is received by a socket formed by the opposing articulating surface.In such a joint, termed an enarthrodial or ball- and-socket joint e.g., the shoulder-joint, hip-joint-the distal bone revolves around an indefinite number of axes, all of which intersect one another at the center of rotation.For simplicity, however, the movement may be described as taking place around axes in the three ordinal planes-viz., a transverse, a sagittal, and a vertical axis.The move- ments around the transverse axis are termed flexion and extension; around the sagittal axis, adduction and abduction; around the vertical axis, rotation.When the bone revolves around the surface of an imaginary cone, the apex df which is the center of rotation and the base the curve described by the hand, the movement is termed circumduction.B. Amphiarthroses.-Inthis division are included all these joints which permit of but slight movement e.g., the intervertebral, the interpubic, and the sacro-iliac joints.The surfaces of the opposing bones are united and held in position largely by the intervention of a firm, elastic disc of fibro-cartilage.Each joint is also strengthened by ligaments.C Synarthroses.-In this division are included all those joints in which the opposing surfaces of the bones are immovably united, and hence do not permit of any movement e.g., the joints between the bones of the skull.Levers.-In the animal machine, as in physical machines generally, work is accomplished by the intermediation of levers.The bones col- lectively constitute a system of levers the fulcra of which lie in the joints.The long bones more especially, are the levers which are employed by the muscles to overcome the opposing forces or resistances.The structure and the chemic composition of the bones, consisting as they do of inorganic matter 67 per cent, and of organic matter 2>S per cent, endow them with both rigidity and elasticity, physical properties which admirably adapt them to the character of the work necessitated by the environment and the organization of the animal.That a lever may be effective as an instrument for the accomplishment of work, it must not only be capable of moving around its fulcrum, but 1 6HUMAN PHYSIOLOGY parallel to one another, and their direction is that of the long axis of the muscle.In length they vary from thirty to forty millimeters, and in diameter from twenty to thirty micromillimeters.Histology of the Skeletal Muscle-Fiber.-Amuscle-fiber consists of a transparent elastic membrane, the sarcolemma, in which is contained the true muscle element.Examined microscopically, the fiber presents a series of alternate dim and bright bands, giving to it a striated appearance.When the bright band is examined with high magnifying powers, a fine, dark line is seen crossing it transversely.It was supposed by Krause to be the optic expression of a membrane attached laterally to the sarcolemma.The muscle-fiber also exhibits a longitudinal striation, indicating that it is composed of fibrillae, placed side by side and embedded in some interfibrillar substance, to which the name sarcoplasm has been given.The fibrillae, which are arranged longitudinally to the long axis of the fiber, are grouped by the intervening material into bundles of varying size, the muscle columns.The fibrillae which extend throughout the length of the fiber are apparently of uniform thickness, passing directly through the transverse membrane and being supported by it.In the region of the dim band the fibrilla presents itself in the form of a homogeneous prismatic rod, termed sarcostyle, separated from neighboring rods by a slight amount of sacroplasm.The Blood Supply.-Theblood supply to the muscle is very great, and the disposition of the capillary vessels, \\ith reference to muscle-fiber, is very characteristic.The arterial vessels, after entering the muscle, are supported by the perimysium; in this situation they give off short, trans- verse branches, which immediately break up into a capillary network of rectangular shape, within which the muscle-fibers are contained.The muscle-fiber in intimate relation with the capillary is bathed with lymph derived from it.Its contractile substance, howev^er, is separated from the lymph by its own investing membrane, through which all interchange of nutritive and waste materials must take place.Lymphatics are pres- ent in muscle, but are confined to the connective tissue, in the spaces of which they have their origin.The Nerve Supply.-Thenerves which carry the stimuli to a muscle enter near its geometric center.Many of the fibers pass directly to the muscle-fibers with which they are connected; others are distributed to blood-vessels.Every muscle-fiber is supplied with a special nerve-fiber, except in those instances where the nerve trunks entering a muscle do not contain so many fibers as the muscle.In such cases the nerve-fibers divide, until the number of branches equals the number of muscle-fibers. 1 8 HUMAN PHYSIOLOGYis not proportional to the weight.While at first it is marked, the elonga- tion diminishes as the weight increases by equal increments, so that the line of extension becomes a curve.In other words, the elasticity of a pas- si ve muscle augments with increased extension.On the contrary the elasticity of an active is less than that of a passive muscle, for it is elon- gated more by the same weight, as shown by experiment.Tonicity is a property of all muscles in the body, in consequence of being normally stretched to a slight extent beyond their natural length.This may be due to the action of antagonistic muscles, or to the elasticity of the parts of the skeleton to which they are attached.This is shown by the shortening of the muscle which takes place when it is divided.Muscular tonus plays an important r61e in muscular contraction.Being always on the stretch, the muscle loses no time in acquiring that degree of tension necessary to its immediate action on the bones.Again, the working power of a muscle is increased by the presence of some resistance to the act of contraction.According to Marey, the amount of work is considerably increased when the muscular energy is transmitted by an elastic body to the mass to be moved, while at the same time, the shock of the contraction is lessened.The position of a passive limb is the result- ant also of the elastic tension of antagonistic groups of muscles.Muscle excitability and contractility are terms employed to denote that property of muscle tissue in virtue of which it contracts or shortens in response to various excitants or stimuli.Though usually associated with the activity of the nervous system, it is nevertheless an independent en- dowment, and persists after all nervous connections are destroyed.If the nerve terminals be destroyed, as they can be by the introduction of curara into the system, the muscles become completely relaxed and quiescent.The strongest stimuli applied to the nerves fail to produce a contraction.Various external stimuli applied directly to the muscle substance produce at once the characteristic contraction.The excitability of muscle is there- fore an inherent property, dependent on its nutrition, and persisting as long as it is supplied with proper